An engine produces a high output, when the inflow of external air into a combustion chamber and the discharge of combustion gas from the combustion chamber are completely and rapidly executed.
However, if the operation of an intake/exhaust valve has a fixed pattern, it is impossible to optimally control the suction of external air and the discharge of combustion gas, according to the engine load.
Thus, recently, the use of a variable valve lift (VVL) has been gradually popularized.
Currently, rocker arm-type apparatuses, which are representative variable valve lift apparatuses, have been proposed. The rocker arm-type apparatuses include one produced by Honda and one produced by Toyota. The Honda's apparatus is constructed so that a rocker arm for a high-speed cam is mounted between two rocker arms, and the connection to the high-speed cam is controlled via a pin, thus converting a lift. The Toyota's apparatus is constructed so that a pin is inserted into a follower of a high-speed cam, which reciprocates while slidably contacting the high-speed cam.
However, since both of the apparatuses are simultaneously connected to two valves (pair of intake valves, pair of exhaust valves), it is impossible to individually control each of the valves. To this end, an additional device is required. Further, the conventional apparatuses are problematic in that they limit the design of a head, due to the interference with a cam journal or the like.
In addition to the above-mentioned type of apparatus, swing arm-type apparatuses which independently control respective valves have been used. However, the swing arm-type apparatus has a problem in that it is difficult to supply hydraulic pressure to a latching system, so that latching reliability is poor. The swing arm-type apparatus has another problem in that it is difficult to ensure sufficient strength, in comparison with the rocker arm-type apparatus.